This invention relates generally to resistance measuring devices and more specifically to a three-terminal resistance measuring device for determining the resistance of sample bulk material. In the art of well logging, for example, it is often necessary to obtain measurements of the resistivity of the wall material and to detect and characterize fractures existing along the wall of the well by resistivity measurements with a three-terminal resistance measuring technique. The change in resistance as sensed by a three-terminal electrode system may be correlated with the size and direction of well wall fractures. It has been a practice in the art to utilize a bulky motor servo system that is extremely slow and too large to lower into a small diameter well. Thus, there is a need for a compact instrument which will rapidly respond to resistance changes in a three-terminal electrode arrangement and which may be remotely operated so that it may be readily employed in well logging for accurate measurements.